Mars Express's kinky radar straightened out

A crooked radar antenna aboard Europe's Mars Express spacecraft has straightened out after being exposed to sunlight for several minutes. The fix gives fresh hope that a second boom will be deployed, allowing the experiment to begin scouting for underground water on Mars.

Mission officials in Darmstadt, Germany, commanded the first of two 20-metre-long fibreglass booms on the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) experiment to pop out of its storage box on 4 May. It had been folded there since before the mission's launch in June 2003.

But engineers studying data from the spacecraft's gyroscopes, which measure its rotation, noticed on 7 May that one of the boom's 13 folded segments had apparently not locked into a straight position as planned. The problem appeared to arise from an outer segment, most likely the tenth.

On Tuesday, Mars Express team members began tests to straighten the boom. They rotated the spacecraft so that the kinked segment was facing the Sun for about 5 minutes, then moved it back into darkness.

On Wednesday, they received telemetry from the gyros showing the action was a success. "The boom is now straight," announced Fred Jansen, the spacecraft's mission manager. "It's a great relief."

Kinks and wrinkles

Jansen says a wrinkle in the fibreglass tube may have hardened into a kink during the nearly two years the craft has spent in the cold vacuum of space. When exposed to heat from the Sun, the wrinkled fibreglass would have expanded, making it more elastic. Then the spacecraft's rotation may have snapped the segment into its correct position.

Team members were initially sceptical about the test's prospects. One acknowledged the day before the test that using the Sun's heat in this way was probably the only hope, and a slim one at that.

And the fix does not guarantee success for MARSIS. The experiment will not be able to function until its other 20 m boom is deployed, completing the 40 m dipole antenna. That deployment was put on hold after an analysis showed the spacecraft could become unstable if a kink occurred on an inner segment of the second boom.

"If the risk is deemed too high, we would have to abandon deployment of the second boom and return to the science mission we had before," Jansen said, before the kink was ironed out.

Whiplash warning

MARSIS was originally scheduled to deploy its booms in April 2004 but was put on hold when computer simulations showed the cold temperatures of space could boost the booms' springiness. Mission managers worried this could make the segments swing out and then back - hitting the craft or wrapping around crucial components.

But ESA decided to proceed with the deployment after subsequent laboratory tests showed that at cold temperatures, the booms sprang out with less energy than predicted - making any strike unlikely to cause damage.

But ironically that means using the Sun to warm the second boom during deployment - to try and avoid any kinks - increases the risk of whiplash.

"So you can't just say you're going to deploy warm," says Jansen.

Scientists hope MARSIS will discover whether the water that once carved canyons on the Red Planet's surface has seeped into underground reserves. If there are underground caches, they may harbour life, or could perhaps be used to supply future crewed missions to Mars.

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